1. Field of the Invention
The present invention relates to a digital-analog converter circuit. More particularly, the present invention relates to a digital-analog converter circuit, which is capable of generating a driving voltage according to a γ curve for correcting optical characteristic of liquid crystals.
2. Description of the Related Art
The liquid crystals are driven by changing a voltage applied thereupon. The relationship between driving voltages and the optical characteristic is generally non-linear. In order to correct this non-linear relationship, a γ voltage is provided to the liquid crystals. Such γ voltage in a low-temperature polysilicon (LTPS) liquid crystal display is constituted by a plurality of resistors in serial connection made on a glass substrate and a plurality of intermediate nodes between these resistors. A γ voltage corresponding to an input data can be extracted from such a structure. The γ voltages forms a voltage curve determined by the characteristic of the liquid crystals.
However, such a voltage curve is determined by the resistors in serial connection made with using an exposure mask, the resistors structure is fixed and cannot be changed anymore. Therefore, despite the change in the characteristic of the liquid crystals due to the change of their material under such condition, in order to change the value of the series resistors, the exposure mask must be remade. Furthermore, due to the optical characteristic of the liquid crystals themselves, the picture quality of the liquid crystals can be changed according to the preferences of the user. However, the conventional technique can not fulfill such demand. In addition, in order to fulfill various demands, respective γ voltage generators with different properties would become necessary, which is an obstacle for device miniaturization and cost reduction. Furthermore, this would worsen the design suitability derived from the concept that one design is applicable to various devices. The design compatibility for a plurality of devices would be difficult, and ultimately leading to the increase of cost.